[Campbell Biology P.745] Based on the life cycle of Schistosoma mansoni and the information ... | Practice Question

Based on the life cycle of Schistosoma mansoni and the information provided, what would be the most likely impact of increased fertilizer runoff into irrigation water on the occurrence of schistosomiasis?

  • A: It would directly increase the number of human infections by enhancing the survival of fertilized fluke eggs in water.
  • B: It would lead to a decrease in schistosomiasis by promoting algal blooms that are toxic to the fluke larvae.
  • C: It would likely increase the incidence of schistosomiasis by promoting the growth of algae, which are a food source for the snail intermediate host.
  • D: It would have no significant impact on schistosomiasis because fertilizer primarily affects plant growth, not parasitic life cycles.

Explanation

The 'WHAT IF?' section states that 'Snails eat algae, whose growth is stimulated by nutrients found in fertilizer.' If more fertilizer runoff leads to more algae, this supports a larger snail population. Since snails are the intermediate hosts for Schistosoma mansoni , an increase in the snail population would lead to more asexual reproduction of the fluke larvae, ultimately increasing the number of motile larvae that escape the snail and can infect humans, thus raising the incidence of schistosomiasis.